#include<stdio.h>
int main()
{
	int i = 0;
	double sum = 0;
	for(i=1;i <= 100;i++)
	{
		if(i%2 == 1)
		{
			sum += 1.0/i;
		}
		else
		{
			sum -= 1.0/i;
		}
	}
	printf("%lf\n", sum);
	return 0;
}
